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When using an antenna tuner on SSB, we could easily add a tone generator and switch to do that.

I have fitted a switchable -6db pad between the output of the pcb and the antenna socket. With the circuit switched in the worst case SWR is about 1.65 to 1 with an open or short circuit. This prevents the finals from ever seeing a poor SWR.

Tune is easily achived with the key down and reduced radiated power when tuning up.

I use 2 watt carbon resistors 33 ohms in a t attenuator circuit. 2 in parallel to give 16.5 ohms which is close enough to the calculated value. A relay is s used to switch this attenuator in and out.

You probably will want to install a pop click fix to eliminate a loud pop whenever TX is turned on and off. This circuit uses a 1N4148 diode, a 470k or 300k resistor, a .22 or .44uF cap and a 2n7000 MOSFET. Joe says this works amazingly well and mounts on the rear of the volume pot as indicated below (ignore the 0.1 uF capacitor).

The first uBITx has appeared with a 2.8” TFT display. The hardware is from Joe VE1BWV and the software from VU2SPF.

The display provides full touch control along with physical optional buttons. 100 memory channels come standard, along with a tunable BFO, selection of VFO A, B or M. All bands are selectable from the front display which is a cheap 2.8” TFT touch display. Joe uses an AT Mega 2560 processor for lots of pins and better performance and an Si5351 for DDS.

We have already done this for the Bitx40 and released software, videos etc.
Under youtube vu2spf and facebook as well as in the [BITX20] io group.
They are for the Bitx40 but the new code for ubitx has all the same features.I have 2 of my 3 Bitx running the basic same code. They work and look great.

This has info on the code, features, hardware, etc. The full UBITX info will be posted soon, including the arduino sketch, hardware options, where to source parts. An article in QRP magazine has just been released to subscribers.

Joe recommends the Elegoo 2.8 inch TFT Display with pen fromAmazon.com. He has ordered 4 over time and the quality has been consistent, resulting in all of them working with clear, clean, crisp displays.

The price is around $15.00 shipped within the USA. Note that the vendor does not ship outside of North America.

The Elegoo 2.8″ display with ATMega 2560 mounted behind it in the uBITx

Arduino Module : Joe uses the AT Mega 2560 and suggests Ebay is the cheapest source at less then $10.00 with any AT mega 2560 working.

DDS module – SI5351 module (not just the chip)- available from Ebay or Adafruit direct or from Amazon.com for around $11.00.

Joe uses female single jacks to solder to the rear of the At Mega. Access to the pins is from the rear of the atmega 2560 as the front is facing the front radio panel with the TFT display plugged directly into it. There is no room to get access to the pins after assembly. This method minimizes the wires from AT Mega to the ubitx board.

You can also use an interface board which VU2SPF has developed – he has the pictures, but no pcb for sale at present.

Jumper cables are as follows:

1 Jumper cable (2 pin) – male to female for connection of SDA and SDC lines from AT Mega to the Si5351 DDS.

1 Jumper female to female 8 pin from atmaga to ubitx board

3 cables for the clocks from Si5351 to the Ubitx. – shielded cable is best

Joe feeds the rig with 13.5 volts – using a well filtered non switching power supply. He also uses 2 “buck” converters (around $1.50 each on Ebay).

The first of these gets fed the 13.5 volt, and reduces the voltage to 9v to feed the AT Mega 2560. This keeps it cooler than running full input voltage. He also adds 2 filter caps – one 2000 mfd capacitor on the input side, and the other on the output side, along with a 2- 10 ohm resistor on the output in series to act as a hash isolation filter.

The second converter is used to feed the SI 5351 module, adjusted to 5 volts. This uses the same filtering system as above.

Joe says this results in a very quiet rig with everything nice and cool.

Arv K7HKL notes that the problem with IRF510 RF amplifiers failing seems to be a recurring one for those who are not quite careful with antenna matching, bias level, and drive level.

As a way to start looking into this situation Arv performed some on-line searches to see how others were working around this problem.

There are a number of potentially useful ideas contained in those articles and discussions, but nothing that obviously applies directly to the problem of blowing IRF510 devices at only a few watts of power if the antenna is mis-matched.

“I destroyed many IRF510 FETs during testing. In fact I blew a small hole in one and another into several pieces. It was quite a shock when the first one was destroyed because it made a loud noise like a rifle being fired.

Once I got tired of replacing the FETs, I built a current sense circuit, which shuts off the bias once the amplifier draws more than about 3 amps from the PSU. I think this circuit is essential. You can build it into the Power Supply or into the Amplifier. I built it into the Amplifier because the power supply, which is also homemade, does not limit until 7 amps. With the current limit circuit the amplifier now survives transmitting into any SWR from an open circuit to a short.”

And Arv K7HKL suggests implementing this bias control circuit used by AC2CZ in his 50 watt IRF510 linear. He suggests you could probably do this using 2N3906 transistors. Arv likes the fact that it includes a warning
light/LED.

John AD0RW who has studied the CW keying issue has determined that the primary problem is that the analogue to digital conversion in the µBitx was having trouble distinguishing between “manual key down” and “dit”. This causes keying errors. For example, an ‘I’ becomes an ‘N’ when the dit paddle is held closed.

John incorporated the keyer code from W0EB and W2CTX into his personal software build, but he was determined to save the last analog input for S/power metering. So he kept the single input that detects four different levels. Actually, he doesn’t care much about straight keying so he left out the manual key resistor.

When looking at the nominal voltage levels with the provided resistors, he observed that there was only around 0.22 volts between the “dit” and “manual key” levels (1.60 vs 1.38 V). On the other hand, there is 1.8 volts between “dit” and “dah”. Errors due to fluctuations would be much more likely between “dit” and “manual key” levels.

He investigated options for resistor replacement, and in the end, replaced the 2.2k resistor with a 5.1k one. Now the nominal levels are 3.4 V for “dah”, 2.6 V for “dit”, and 2.1 V for “both”. The boundary ADC values were adjusted in the software.

He has found the results to be favourable so far in his testing, including sending a fair amount of practice code at speeds up to 25 wpm. The iambic action seems flawless and smooth.

He notes that “I might actually get good at sending iambic style someday…”. Some of us need to try this solution. Saving ports is a good idea on an Arduino Nano! It would also be helpful to know what values folk are using for the thresholds for the boundary points in the sketch.

Reference

A mod developed by Gary N3GO (and required for Full QSK) also mitigates the Tx and Rx pop/thump noises in SSB mode. This mod should work fine with the existing relays and with or without other mods, but has yet to be verified by others.

Martin Held AE7EU has been very busy designing a top tier board for the µBitx main board.

The board interfaces via the standard connectors to the main board of the uBitx. Martin’s top board adds essential features, such as speech compression, an integrated Teensy 3.2 processor, an attenuator and an auto antenna tuner. The front panel break-off from the board simplifies construction and makes the form factor as small as possible.

We look forward to seeing Martin’s report on how the board performs in practice. It is likely we will see a few changes to the board before it becomes available to purchase!

In a post to the BITX20 list Martin identified four options for release:

Tired of searching through the Bitx20 iogroups emails to find mods for your µBitx transceiver?

This website should make it much easier to identify potential mods for your own µBitx, and get the information you need to do the construction! It is not intended to replace the group culture, but to make it easier to reference mods suggested by group members.